The invention relates to an image display and pick-up apparatus comprising:
a screen switchable between a transmissive state and a diffusing state and having a front side and a rear side; PA1 a projection unit arranged at the rear side of the screen for projecting an image on the screen, which image is viewed from the front side; PA1 a pick-up unit arranged at the rear side of the screen and facing the rear side at a predetermined angle for picking up, through the screen an image of an object located at the front side of the screen.
Such apparatus is known from, for example, EP-A 0 454 244 to which U.S. Pat. No. 5,282,027 corresponds, and is shown schematically in FIG. 2a. In the videophone monitor of FIG. 2a, at the rear side of a screen 9 of a videophone monitor 1, a projecting unit 8 consisting of a lamp 2, a reflector 3, a condenser lens 4, a shutter 5, a liquid crystal device (LCD) 6 which is a display device of a transmission type and a projection lens 7 are arranged on an optical axis 10. At the rear side of the screen 9, there is a/so arranged a pick-up unit 11 consisting of a CCD camera or the like. The pick-up unit 11 is not located on the optical axis 10, but in the vicinity of the projection lens 7 such that the field of view of the projection lens 7 and that of the pick-up unit 11 are substantially the same.
Light emitted from the lamp 2 is reflected by the reflector 3 and converted into a parallel light beam by the condenser lens 4. When an image is to be displayed, the shutter 5 is in the transmission state, so that the light beam passes through it and is incident on the LCD screen. The fight beam is then modulated with the information of the image on the LCD device and the modulated beam passes through the projection lens 7 to the projection screen 9. The lens projects an image of the LCD display on the screen.
As described in EP-A 0 454 244 the projection screen is switchable between two states. FIG. 2b shows an embodiment of such screen. The screen may comprise a plate of transparent material wherein small particles 13, for example spheres, are embedded. These spheres consist of a material, the refractive index of which can be switched between a first value different from that of the plate material and a second value equal to that of the plate material. If the refractive index of the particles 13 is different from that of the plate material, these particles act as diffusing particles and the projection screen is then in the diffusing state. This is represented in FIG. 2b by the shaded spheres. If the refractive index of the particles 13 is equal to that of the plate material, represented in FIG. 2b by the open spheres, the projection screen is in a fully transmissive state.
The shutter 5 and the projection screens are controlled synchronously. If an image is to be displayed towards the user 12, the shutter is set in the transmissive state and the screen in the diffusing state. If an image of the user 12 is to be taken, the shutter is closed and the screen is set in the transmissive state. The particles 13 may consist of a liquid crystal material. It is also possible that the screen 9 comprises an EC material or an electro-conductive polymer.
FIG. 3 illustrates what the user, looking at the videophone monitor, sees during the pick-up state, i.e. when the shutter 5 is closed. As in this state the projector 8 emits no light, the brightness of the screen is low and the user 12 can look through the screen and can see the structure at the rear side of the screen. The user can see then a lens surface 11a of the pick-up unit 11 and a lens surface 7a of the projection lens 7.
During use of the videophone monitor the projection screen 9 is periodically switched between the diffusing state and the transmissive state. As during the pick-up state the user can see the projection lens surface 7a, he may see a delayed projected image and mix this up with the projected image of the subsequent state, i.e. a projection state.
Moreover, when the screen 9 is set in the diffusing state, an ambient fight incident on front surface side of the screen 9 is diffusely reflected by the particles 13 towards the user 12. So that the contrast of the projected image decreases.